We propose to carry out experiments to obtain basic information on the mode of action of LH-releasing hormone (LH-RH) using pure natural LH-RH, synthetic LH-RH and its analogues. The first phase of the studies is aimed at the investigation of the pituitary responsiveness to LH-RH, with special emphasis on factors and conditions (experimental or physiological) which may modify the pituitary responsiveness. Among these factors, interaction of LH-RH and gonadal steroids will be extensively examined. The second phase of the studies would consist of efforts to produce specific antiserum to LH-RH and to establish a radioimmunoassay method for LH-RH. The, the metabolic fate of exogenously administered LH-RH will be investigated in connection with the magnitude and duration of stimulation of LH release from the pituitary. Anti-LH-RH serum will also be used to study its effect on endogenous LH-RH. Possibility of neutralization of endogenous LH-RH by anti-LH-RH and prevention of ovulation by anti-LH-RH will be investigated. The third phase of experiments will be the investigation in experimental animals of the influence of artificially induced LH surge by administration of LH-RH during the early follicular stage on physiological preovulatory surge of LH and ovulation. This investigation will shed light on the possibility of a new contraceptive approach by porcine LH-RH early in the cycle. The fourth phase of the experiments will be a study of the mechanism of action of LH-RH with special emphasis in structure-function relationship of LH-RH, using synthetic LH-RH and its analogues.